* I do a lot of automation recording via record in the arrange view with my midi controllers and it's not uncommon that I touch a knob/ xy-controller/joysticks by accident in "combat" and so I have to undo the whole automation recording.
If you have already recorded 3 minutes automation data and have to undo it only because another automation is falsified it's a bit annoying.
* I sometimes use reaktor as a midi LFOs to modulate some things in live (loopback via midi yoke) and in this case I cant prevent the track to record automation data when I hit record.
* If you have a lot of automation data and over dub it, it's a bit stressful to watch that really only the automation is recorded which you want.
edit: /added this point)
* sometimes old knobs send some unwanted data (say the knob jumps between the value 33-34 sometimes) even when you don't touch them, This is no real problem when you tweak them, but if you don't touch them and record automation, just one fluctuation from them and they will record unwanted stuff or overwrite the existing automation data.
I have this on one knob from my uc - 16 and my pitchbend for example.
I think you get what my point is? It would be calming to foreclose such things.